Tubulin is present in nerve endings both as formed microtubules and in a form that is tightly associated with the synaptic plasma membrane. We are studying the interrelationship of these two forms of tubulin. In particular, our major effort is directed towards further study of the conditions under which tubulin can be polymerized in vitro directly into membrane vesicles. We are also studying the protein subunit structure of brain intermediate sized filaments and analyzing synaptic subfractions for this protein. BIBLIOGRAPHIC REFERENCES: Feit H, Neudeck U and Baskin F: (1977), Comparison of the isoelectric and molecular weight properties of tubulin subunits. Journal of Neurochem, in press. Feit H, Kelly P and Cotman C; (1977), The identification of a protein related to tubulin in the post synaptic density. Proc. Nat. Acad. Sci. 74:1047-1051.